The present invention relates to an electromagnetic adjusting device, in particular for automatic transmissions in motor vehicles.
In such electromagnetic adjusting devices, the magnetic force produced by an electromagnet performs hydraulic regulating functions. The dependency between the excitation current supplied to the magnetic coil and the control regulating pressure is described by the regulating pressure-current characteristic line of the adjusting device. The line extends constantly, is specific, and forms the basis for the application in a motor vehicle. A substantial feature of the characteristic line is its slope. This slope is determined by the properties of the electromagnet. Fluctuations in the manufacturing tolerances for the components of the electromagnet act on the magnetic flux and thereby on the magnetic force so that in the characteristic lines of the same electromagnetic adjusting devices of one manufacturing series considerable fluctuations in the characteristic line slope can occur.
In known electromagnetic adjusting device with a proportional magnet for actuating of proportional valves as disclosed in the European patent document EP 0 464 370, for elimination of the negative influence of manufacturing dispersion and permeability differences of the magnetic material on the magnetic force of the proportional magnets and thereby on the slope of the characteristic line, means are provided with which the magnetic resistance of the magnetic circuit can be changed also after the assembly of the electromagnetic or the electromagnetics adjusting device within certain limits. Therefore the electromagnet can be post-adjusted with respect to its magnetic force. These means have an axially engaging ferromagnetic adjusting sleeve which is axially displaceable and with its portion that covers or overlaps the central part produces a magnetically well conductive connection between the central part and the housing body. The adjusting sleeve for this purpose is screwable in a central opening in the housing body. Depending on the size of the sleeve portion covering the central part, the magnetic flux in the magnetic circuit can provide a more or less greater portion to be available and thereby changes the magnetic resistance which counteracts the magnetic flux. The size of the covering or overlapping determines the height of the magnetic conductive value and influences thereby the total magnetic resistance.
Accordingly, it is an object of the present invention to provide an electromagnetic adjusting device which avoids the disadvantages of the prior art.
In keeping with these objects and with others which will become apparent after, one feature of the present invention resides, briefly stated, in an electromagnet having a magnetic coil; a substantially cup-shaped housing which surrounds said magnetic coil and is composed of a ferromagnetic material, said housing having a housing bottom, a ferromagnetic central part which extends from said housing bottom and supports said magnetic coil, and a movable armature located before said central part and leaving a working air gap so as to form with said housing and said central part a magnetic circuit which has a magnetic resistance for a magnetic flux; and means for changing the magnetic resistance, said means for changing the magnetic resistance including an axial depression provided in said central part and an axially displaceable ferromagnetic filling member inserted in said depression and limiting with a bottom of said depression an auxiliary air gap.
When the electromagnetic adjusting device is designed in accordance with the present invention it has the advantage that the iron cross section which is available for the magnetic flux remains unchanged during the post adjustment of the electromagnet and an adjustable electromagnetic resistance is connected parallel to the constant magnetic resistance of the magnetic circuit. Thereby the adjusting of the magnetic force can be performed very finely.
The inventive features for forming the adjusting means are structurally simple and can be produced in a cost favorable manner. The performed adjustment can be fixed in a simple additional means, so that in rough operation a deadjustment of the electromagnetic adjusting device does not occur.
In accordance with another feature of the present invention a shaped member is welded with a coating which covers a housing button and is composed for example of a non-magnetic material, such as plastic. With this feature a price-favorable construction that is particularly simple for manufacturing can be provided for adjusting of the electromagnet.
The novel features which are considered as characteristic for the present invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.